Diseases characterized by inflammation, excessive secretion and obstruction of the airways affect a substantial segment of the population. The respiratory epithelium is a complex physical and biochemical barrier that plays a vital role in host defense and acts as a central modulator of inflammation. Perturbation of this barrier, as occurs in both acute and chronic injurious states, results in airway production of chemokines, cytokines and growth factors. Interleukin-8 (IL-8), a powerful chemoattractant for neutrophils, is synthesized and released from airway epithelial cells in response to irritants, infectious agents and inflammatory modulators and plays a central role in pulmonary inflammatory processes. Alveolar and bronchial epithelial cells (BEpC) are considered to interact with immune cells by direct adhesion and respond to humoral factors including lipid mediators. Sphingosine-l-phosphate (SIP), a potent bioactive sphingolipid metabolite, has been implicated in regulating a wide range of cellular responses such as differentiation, angiogenesis, mitogenesis and apoptosis. BEpC are known to express endothelial differentiation gene (EDG) receptors, which are heterotrimeric G-protein coupled and specifically bind SIP with high affinity. Although some critical cellular functions of SIP have been recognized, little is known about the role of SIP as an inflammatory mediator. Preliminary results suggest that SIP is a potent stimulator of IL-8 secretion in BEpC, which leads to the following hypothesis: SIP is a regulator of pulmonary inflammation by mediating IL-8 secretion in BEpC. To test this hypothesis, the effect of SIP on IL-8 secretion from primary and immortalized BEpC will be investigated in the following specific aims. Specific Aim #1: To characterize the SlP-induced secretion of IL-8 in BEpC by studying EDG receptor involvement and Gprotein coupling. Specific Aim #2: To identify the intracellular signaling pathways that regulate SIP-mediated IL-8 secretion, focusin on the roles of protein kinase C, calcium, mito en activated protein kinases, hos holi ase D, and NfkappaB.